Dihydrosterculic acid (DHS) is a fatty acid containing a ‘mid-chain’ cyclopropane ring structure that can be processed into industrial oils with the rare combination of high oxidative stability and low melting points (Kinsman, 1979; Zhang et al., 2004).
Although routes for the chemical synthesis of DHS are known, these reactions generate a series of side-products requiring purification procedures (Zhang et al., 2004). In contrast, biological routes of synthesis accurately generate cyclopropanated fatty acids from membrane-bound 18:1 by cyclopropanated synthetases (CPFAS) isolated from various plants (Bao et al., 2002) and bacteria (Wang et al., 1992).
The plant CPFAS isolated from Sterculia foetida, and likely all plant CPFAS enzymes, are atypical lipid modifying enzymes by virtue of using 18:1 at the sn1 position of PC (Bao et al., 2003), rather than the acyl-groups attached to the sn2 position of PC, such as FAD2 (Stymne and Appelqvist, 1978). The DHS formed in transgenic tobacco cell lines was found predominantly on the PC fraction, suggesting that sn1-bound DHS is not easily moved into neutral lipid fractions, such as the glycerol backbone of triacylglycerides (TAG, (Bao et al., 2002)). Recently a cotton CPFAS (GhCPFAS) expressed in Arabidopsis seed produced ˜1% DHS in seed lipid analysis (Yu et al., 2011), suggesting that the transfer of DHS from the site of synthesis on PC into seed oil is problematic.
There is a need for recombinant cells with enhanced levels of DHS production.